This invention relates generally to methods and apparatus for CT imaging and other radiation imaging systems, and more particularly to detecting and correcting data for tube-spit events.
In at least some computed tomography (CT) imaging system configurations, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the “imaging plane”. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal spot. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator adjacent the collimator, and photodetectors adjacent the scintillator.
The term “tube-spit” refers to temporary electrical short-circuit that sometimes occurs inside an x-ray tube. Typically, upon the occurrence of tube-spit, the supply of power to the x-ray tube is temporarily interrupted to prevent arcing. Power is restored to the tube after a time interval of, for example, about one millisecond. During tube-spit recovery, no x-ray photon is emitted from the x-ray tube. As a result, detector measurements taken during the recovery are invalid.
Generally, tube-spit recovery time should be shorter than the data acquisition sampling interval to avoid image artifacts. As data sampling rates increase, a recovery time of about one millisecond is too long to avoid artifact generation.